HELP: Grinding, ROARING rotating sound coming from rear
 

Was on a high speed run on an open stretch of highway. Got up to about 105. I had to brake fairly heavily at one point because of traffic but nothing serious or emergency type braking. Since that point, it was about 10 mins until I got to my exit. Got off the highway and while slowing down on the off ramp, the car just jerked and slowed down big time as it down shifted. Since then there's a really LOUD rotational noise coming from the rear.

Symptoms include:
My entire neighborhood can hear it
Is speed sensitive
More prominent and apparent throughout the cabin at speeds below 20mph
Above 20mph, it fades a bit
Taking my foot off the gas at speed takes the noise out of the cabin but as soon as the car/suspension settles, it returns to the cabin.
Putting the car in neutral doesn't change the presence of the sound. It goes away slightly but only because i'm taking my foot off the gas. [same sound level]
Engaging drive again, the sound immediately returns to the cabin.
Sounds also like i've got a flat or running on off road tires.
Strong smell of gear oil

Jacked up the rear end and I tried the wheel bearing test of holding the wheel at 12 & 6 and 9 & 3 to move it but there's no movement. Rotating the wheel I hear a scraping noise almost like the pad is contacting the rotor surface. I hear this on both sides.

I've also drained the differential after my short (1mile) drive this morning and the fluid was black. When i did the drain and fill on the weekend prior, i did it cold. For the service I used Valvoline SynPower [full synth] 75w-90. It took approx. 3/4 quart. Today however only 1/4 quart came out..... I stopped the collection when it became a trickle instead of a steady stream.

I've also recently done a brake job with new pads all around, new rotors on the front only and fresh brake fluid.

Some vids:
Noise from inside the cabin

Diff Fluid

Right wheel turning by hand

Left wheel turning by hand

Right side of differential

Front of differential

FINAL UPDATE: This turned out to be my rear differential. It was replaced with a used unit and the car is functioning properly again.

Sound like you got hit in the rear with another car? is that what it sound like?
Your tranny is gone.

Not sure what getting hit in the rear sounds like......but it seems to upshift and downshift OK.

Took it for a drive down the street, popped it in neutral and the sound is still there. Reverse and drive engage like normal. My brother said it sounds like when his differential went. Given the strong smell of gear fluid, that might not be a far fetched idea.

Sorry to hear .. literally. Definitely sounds bad but sounds more like the differential or axle but not the tranny. Just a guess of course. Have you checked your diff. since? Sure there's no leak?

I'm sure more knowlegeable people will post. Good luck and hope its not gonna be too expensive.

You said you just did a rear diff fluid change... was this before or after the problem happened. If it was before, I'd go back and drain the fluid into a clean pan so you can see if there is any signs of metal in there, or worse if the fluid was lost somehow. (I recently replaced the rear diff of an E46 that had the fluid changed at an indy out of state, then drove over a thousand miles to La with the drain plug loose and lost the fluid. the diff was TOAST)

If the rear diff fluid is good you should take a small sample of the trans fluid to analyze as well. (a couple ounces) Also, If one of the rear bearings is going out and has a bunch of slack it can cause grinding noises and real weird brake feel, but you would know if that was the case... I suspect the rear diff myself from listening to the video.

'06 - are you still under warranty?

The diff drain and fill was before the problem. Problem started just this afternoon and I did the drain and fill this past Sunday. It's been 2 days and I've been back and forth to work for 2 days, about 70 miles on the new fluid.

Warranty was up 2 days ago! I bought it used, as-is but the drivetrain warranty is up.

If the warranty is only up for 2 days, they should be able to goodwill the repair.

The dealership is about 75 miles away.... not sure if it would make it.